The invention relates to the field of power supply circuits and, more particularly, to a power supply circuit for an automobile for use in connection with motor driven accessories, such as windows, a sun roof or the like.
With the advent of luxury automobiles, many accessories which were previously mechanically operated have now been provided with a motorized drive mechanism. For example, it is well known to equip an automobile with windows which are motor driven or with a sun roof likewise motorized.
The power needed to drive these motors is typically derived from the battery in the vehicle. In a typical installation, the accessory motor is connected to the ignition switch so as to be operative only when the vehicle is turned on. This avoids the potential of inadvertent discharge of the battery of an unattended vehicle and other safety-related problems. In such installations, a relay is provided which operates in response to the turning-on of the vehicle ignition switch to apply power from the battery to the drive motor of the accessory. Once the ignition is switched off, the relay is de-energized and the accessory can no longer be operated.
This arrangement creates an inconvenience, however, in the event the driver desires to operate the accessory after turning off the the ignition switch. For example, a driver may turn off the vehicle and only then notice that certain windows are left open. In prior art devices, however, the window cannot be closed via the accessory motor unless the ignition switch is again turned on. This step thus created an inconvenience to the driver.
Accordingly, a problem exists in such prior art devices in that power to the accessory motor was terminated with turning off of the ignition switch, whereas many occasions arise in which it is desirable to still have power available for such motors even after the ignition has been turned off.